The paper presents the analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV technique, pressure probe traverses and numerical simulations. PIV measurements have been performed at different heights inside one diffuser channel passage for a given speed of rotation and various mass flow rates. For each operating condition, PIV measurements have been made for different angular positions of the impeller. For each angular position, instantaneous velocities charts have been obtained on two simultaneous views, which allows, firstly, to cover the space between the leading edge of the impeller and the diffuser throat and secondly, to get a rather good evaluation of phase averaged velocity charts and “fluctuating rates “. Probe traverses have also been performed using a 3 holes pressure probe from hub to shroud diffuser width at different radial locations in between the two diffuser geometrical throats. The numerical simulations were realized with the two commercial codes: i-Star CCM+ 7.02.011 (at LML), ii-CFX 10.0 (at University of Padova). Fully unsteady calculations of the whole pump were performed.  Comparisons between numerical and experimental results are presented and discussed for two mass flow rates. In this respect, the effects of fluid leakage due to the gap between the rotating and fixed part of the pump model are analysed and discussed

BAYEUL-LAINE, Annie-Claude

BOIS, Gérard

CAVAZZINI, Giovanna

CHERDIEU, Patrick

DAZIN, Antoine

DUPONT, Patrick

ROUSSETTE, Olivier

I-Revues

21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
  1 
NUMERICAL AND EXPERIMENTAL INVESTIGATIONS 
IN A VANED DIFFUSER OF SHF IMPELLER: FLUID 
LEAKAGE EFFECT 
A. C. BAYEUL-LAINE
a
, P. DUPONT
b
, G. CAVAZZINI
c
, P. CHERDIEU
b
, A. DAZIN
a
 , G. BOIS
a
,                      
O. ROUSSETTE
g
  
a. Arts et Métiers PARISTECH, LML, UMR CNRS 8107, Bd Paul Langevin, 59655 VILLENEUVE D’ASCQ 
b. Ecole Centrale de Lille, LML, UMR CNRS 8107, Bd Paul Langevin, 59655 VILLENEUVE D’ASCQ 
c.
 
University of Padova, Energy and Fluids, Department if Industrial Engineering 
Résumé 
Le papier présente l’analyse des performances et de l’écoulement interne dans un diffuseur aubé d’une 
pompe centrifuge grâce à la technique PIV, aux sondes de pression et aux simulations numériques. Les 
mesures PIV ont été réalisées à différentes hauteurs dans un canal du diffuseur, pour une vitesse de rotation 
et différents débits. Dans chaque cas, les mesures PIV ont été effectuées pour différentes positions angulaires 
de la roue. Des sondes de pression trois trous ont également été utilisées dans le diffuseur à différentes 
positions radiales et axiales. Les simulations numériques ont été réalisées avec deux codes: i-Star CCM+ 
7.02.011 (LML), ii-CFX 10.0 (Université de Padoue). Des comparaisons entre résultats numériques 
(modélisation instationnaire) et expérimentaux sont présentés et discutés pour deux débits. Les effets des 
pertes dues aux jeux entre parties fixes et partie tournante sont étudiés. 
Abstract 
The paper presents the analysis of the performance and the internal flow behaviour in the vaned diffuser of a 
radial flow pump using PIV (particles image velocimetry) technique, pressure probe traverses and numerical 
simulations. PIV measurements have been performed at different heights inside one diffuser channel 
passage for a given speed of rotation and various flow rates. For each operating condition, PIV 
measurements have been made for different angular positions of the impeller. Probe traverses have also 
been performed using a 3 holes pressure probe from hub to shroud diffuser width at different radial 
locations in between the two diffuser geometrical throats. The numerical simulations were realized with the 
two commercial codes: i-Star CCM+ 7.02.011 (LML), ii-CFX 10.0 (University of Padova. Comparisons 
between numerical (fully unsteady calculations) and experimental results are presented and discussed 
for two flow rates. In this respect, the effects of fluid leakage due to the gap between the rotating and fixed 
part of the pump model are analysed and discussed. 
Keywords: Pump, diffuser, PIV measurements, numerical calculations, probes 
1 Introduction 
Flow behaviour in a radial machine is quite complex and is strongly depending on rotor stator interactions 
and operating conditions [1-3].  
In numerical simulation, two aspects have to be considered, the first one concerns the governing equations 
which are solved in the model: three kinds of numerical calculations are currently used in turbo machinery (i-
frozen rotor calculations, ii-mixing plane calculations, iii-unsteady calculations). The second aspect concerns 
the geometrical model. Some geometrical simplifications are currently used. For example, the leakage flows 
are often neglected. It is obvious that a complex model (fully unsteady, with leakage flows) will be more 
time consuming but closer to the real physics. In this paper, some limits of the numerical models are pointed 
out. To do so, two numerical calculations are compared to experimental results for two flow rates. 
The test model corresponds to the so-called SHF pump, working with air, in similarity conditions compared 
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
  2 
to water, for which several studies have been made [4-10] involving numerical and PIV comparisons. Figure 
1 shows SHF impeller. The existing database has been completed by pressure probe measurements for a 
complete flow performance analysis. These measurements are compared to several numerical calculations in 
the present paper. 
2 Experiments 
2.1 Test and apparatus 
Test pump model and PIV measurements conditions have been already described in several papers as ref [4, 
5 and 6] and main pump characteristics are given in table 1. This set-up allows the existence of a “positive” 
leakage flow going into the gap between impeller outlet section and inlet vaned diffuser section which is 
specific to the experimental set-up. This is due to the fact that the pump outlet corresponds to atmospheric 
conditions. 
The PIV results come from the thesis of G. Cavazzini [9]. 
Table 1 : Pump characteristics 
Impeller  Diffuser  
Inlet radius R1  = 0.14113 m Inlet radius R3  = 0.25956 m 
Outlet radius R2  = 0.25956 m Outlet radius R4  = 0.44 m 
Number of blades Zi  = 7 Number of vanes Zd  = 8 
Outlet height B2  = 0.04 m Height B3  = 0.04 m  
Impeller design flow rate Qi  = 0.337m
3
/s Diffuser design flow rate Qd = 0.8Qi 
Rotation speed N  = 1710 rpm Impeller-Diffuser radial gap 1 mm 
2.2 Three holes probes 
A three holes probe has been used to make hub to shroud traverses. Using a specific calibration one can get 
total pressure, static pressure, absolute velocity and its two components in radial and tangential direction. 
In order to well represent the flow field, twenty-three probe locations are defined as it can be seen in figure 1. 
For each location, ten axial positions are registered (b*=0.125, 0.2, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 0.925, 
0.975 from hub to shroud). The present analysis focuses only on locations 19 to 23 in the blade to blade 
channel of the diffuser. 
2.3 General flow conditions 
All types of measurements have been performed for several flow rates. But, results presented in this paper 
refer only to two flow rates, a one  close to the design point of the vaned diffuser Q*=0.766 which is 
different to impeller design flow rate Q*=1 (the vaned diffuser design was chosen in order to allow an 
enlarge pump performance characteristic curve for low flow rates). The second normalised flow rate is equal 
to 1.134. 
3 Calculations 
Frozen rotor and unsteady calculations were performed using Star CCM+ code and results are compared with 
already published CFX results [7, 8].  
3.1 Star CCM+ 
The calculation domain was divided into three zones: the inlet zone, the impeller zone and the diffuser zone. 
The boundary condition at the inlet consisted of a flow rate. The boundary condition at the outlet was the 
atmospheric pressure. The fluid (air) was considered incompressible at a constant temperature of 20ºC. A 
polyhedral mesh with prism layers is used for all calculations (5 prism layers for a total prism layer thickness 
of 1 mm). The target size is 3 mm and the minimum size 0,5 mm . The size of the grid is about 3. 10
6
 cells. 
The SST k- turbulence model is used. 
Line probes are plotted as defined in figure 1 in order to obtain all parameters (pressure, total pressure, radial, 
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
  3 
tangential and axial velocity and velocity magnitude) for different impeller angular positions relative to the 
diffuser vanes (Figure 2). In this paper, P3 is the only position presented and discussed. 
The convergence criteria are less than 1.e
-4
. Maximum values of y+ are around 15, and mainly below 9 in 
the whole computational domain. A time step, corresponding to an angular rotation of 1°, has been chosen. 
    
FIG. 1 - Diffuser 
measurement locations for 
probe traverse and unsteady 
calculations 
FIG.2 - Impeller different 
angular positions relative to 
the diffuser vanes 
FIG.3 – Seal 
system at the 
impeller inlet 
FIG. 4 – Seal system 
at the impeller outlet 
3.2 CFX 
In order to investigate the influence of leakage flows, numerical results obtained using CFX are also 
presented. G. Cavazzini et al [7, 8] proposed two kinds of unsteady simulations, with and without leakage 
flows.  
As regards the simulations considering the leakage flows, the seal systems both at the impeller inlet and 
outlet were modelled (Figures 3, 4). At the labyrinth of the seal system close to the impeller inlet the mass 
flow rates determined from the experimental data was prescribed, assuming stochastic fluctuations of the 
velocities with 5 % free-stream turbulence intensity. At the impeller outlet the leakage mass flow rate was 
controlled by the known experimental pressure in the large plenums upstream the labyrinth. 
Much more details on model, mesh and numerical simulations are reported in ref [8]. 
3.3 Results and comparisons 
   
FIG.5 - Pump non-dimensional 
total head curve 
FIG.6 - Pump non-dimensional  
isentropic head curve 
FIG.7 - Pump non-dimensional  
static head curve 
Global results of total theoretical head pump are in good agreement between Euler one dimensional approach 
and frozen rotor calculation. Unsteady calculation results, performed for the two non-dimensional flow rates, 
give the same level, as it can be seen in figures 5 and 6. One can note, figure 7 that the numerical static 
pressures underestimate the experimental pressure rise, whatever the numerical scheme adopted. This is 
particularly obvious for Q/Q*>1. At these flow rates, previous studies [8, 9, and 10] have shown a strong 
boundary layer detachment at the diffuser vane leading edge.  The calculations may have some difficulties to 
predict correctly the flow behaviour in these regions and thus overestimate the losses linked with these 
phenomena. One can nevertheless note that the consideration of the leakages seems to improve slightly the 
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
  4 
performance prediction. 
Local results are analysed for unsteady calculations, three holes probes and PIV measurements. 
Figure 8 gives the contours of radial and tangential velocities, for b*=0.5 at mid height inside the diffuser 
channel passage for the angular position P3 of the impeller and for the diffuser design flow rate. The PIV 
experiments are compared to unsteady Star CCM+ calculations. 
The radial and velocity contours at this flow rate and for the two angular positions of the impeller are very 
similar for the numerical results and the PIV measurements, but with a lower magnitude of velocities in case 
of calculation. The examination of the contours of tangential velocity for the same flow rate and for the two 
angular positions leads to same comments. This tendency has also been observed for other value of b* by 
comparison between numerical calculation and between PIV done by G. Cavazzini [9]. This leads to suppose 
a higher flow rate at the outlet for the case of measurements. As the experimental results have been 
performed with pump configuration with leakage, it can be supposed that there is a positive leakage between 
impeller and diffuser. 
STAR 
CCM+ 
 
 
 
 
 
 
 
PIV [9] 
 
 
 
  
Vr (m/s) 
 
 
Vu (m/s) 
FIG. 8 - Contours of velocities - Q*=0.776 –  b*=0.5 -  Angular position P3                                                  
On the contrary, it has been observed, for the radial and tangential velocities contours for high flow rate that 
the tendency inverses. So it can be supposed that fluid leakages are negative in this case. 
Radial velocity evolutions of unsteady calculations without leakage (obtained from the two different codes: 
“CCM+” and “CFX 1”), and unsteady calculations with leakage (obtained only from CFX [7]: “CFX 2”) are 
presented in figures 9 and 10 for both flow rates. PIV measurements (“PIV”), and three-hole pressure probes 
(“probes”) results are plotted on the same figures. Results present time-averaged values of radial and 
tangential velocities distribution from hub to shroud section as a function of radius. 
The influence of leakage can be confirmed when comparing numerical results obtained without and with 
leakage. Experimental results are in better agreement with calculations obtained with leakage. This can be 
mainly seen on radial velocity distribution shown in figures 9 and 10. For Q*=0.776, the mean relative 
difference between experimental and unsteady calculations radial velocities is about 30% for calculations 
without leakage and 13% for calculations with leakage. On the contrary for Q*= 1.134 numerical results 
without leakage are higher than experimental ones. The mean relative difference is about -17% for 
calculations without leakage and 5% for calculations with leakage.  
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
  5 
These results must be more deeply analysed, in particular PIV ones; they strongly depend on impeller 
position during its rotation and only time-averaged values are presented here. Pressure probe results are also 
depending on unsteady effects and this has to be taken into account for further data reduction analysis. 
 
 
b*=0,125 
 
 
b*=0,250 
 
 
b*=0,500 
 
 
b*=0.750 
 
 
 
b*=0.875 
 
 
FIG. 9 - Non-dimensional radial 
velocity Vr* with R* - Numerical-
Experimental comparisons in 
horizontal cut planes - Q*=0.776 
 FIG. 10 - Non-dimensional radial 
velocity Vr* with R* - Numerical-
Experimental comparisons in 
horizontal cut planes- Q*=1.134 
5. Conclusions 
Comparisons between two numerical 3D approaches and PIV measurements have been presented inside the 
diffuser of a centrifugal impeller at different cut planes inside the diffuser. Two different impeller blade 
positions were considered. Two flow rates were studied. 
The contours of radial and tangential velocity at mid height as well as the time-averaged values of radial and 
tangential velocity distributions allow leakage to be an important parameter that has to be taken into account 
in order to make good comparisons between numerical and experiments. Henceforth, simulations with fluid 
leakages will be realized and unsteady probes will be used in order to confirm these previous results. These 
21
ème
 Congrès Français de Mécanique                                                                  Bordeaux, 26 au 30 août 2013 
  6 
calculations show few influence of taken account fluid leakage on global performance but a real 
improvement concerning velocity distributions. 
Nomenclature 
 b*  [-] Non-dimensional distance from hub 
 C  [mN] Impeller torque 
 p  [Pa] Pressure 
 pt  [Pa] Total pressure 
 Q* Q/Qi [m
3
/s] Non-dimensional volume flow rate at impeller’s inlet 
 Qd  [m
3
/s] Diffuser design flow rate 
 Qi  [m
3
/s] Impeller design flow rate 
 R  [m] Radius 
 R* R/R2 [-] Non-dimensional radius 
 Vr* vr/U2 [-] Non-dimensional radial velocity 
 Vu* vu/U2 [-] Non-dimensional tangential velocity 
 U2 R2 [m/s] Frame velocity at impeller outlet 
   [kg/m
3
] Air density 
   [rad/s] Angular Velocity 
 
tc
  dpt/(U2
2
/2) [-] Non-dimensional total pump head  
 
ti
  CQ U2
2
/2) [-] Non-dimensional isentropic head 
Index 1   Impeller inlet 
 2   Impeller outlet 
 3   Diffuser outlet 
References 
[1] Adamczyk J. J., Celestina M. L., Chen J. P., 1994, « Wake induced unsteady flows :their impact on rotor 
performance and wake rectification », ASME International Gas Turbine and Aeroengine Congress and 
Exposition, The Hague, Netherlands, June 13-16, paper 94GT219. 
[2] Arndt N., Acosta A.J., Brennen C.E., Caughey T.K, 1990, « Experimental Investigation of Rotor – Stator 
Interaction in a Centrifugal Pump With Several Vaned Diffusers », ASME Journal of Turbomachinery, Vol. 
112, p. 98-108. 
[3] Eisele K., Zhang Z., Casey M. V., Gülich J., Schachenmann A., 1997, « Flow analysis in a Pump 
Diffuser Part 1 : LDA and PTV Measurements of the Unsteady Flow », Transactions of ASME, Journal of 
Fluids Engineering, Vol. 119, p. 968-977. 
[4] Wuibaut G., Dupont P., Caignaert G., Stanislas M., 2000, « Experimental analysis of velocities in the 
outlet part of a radial flow pump impeller and the vaneless diffuser using particle image velocimetry », 
Proceedings of the XX IAHR Symposium, Charlotte (USA), 6-9 august, paper GU-03. 
[5] G. Wuibaut, G. Bois, M. El Hajem, A. Akhras, J.Y. Champagne, Optical PIV and LDV “Comparisons of 
Internal Flow Investigations in SHF Impeller”, Int. J. of Rotating Machinery, 1-9, 2006 
[6] A. Dazin, O. Coutier-Delgosha, P. Dupont, S. Coudert, G. caignaert, G. Bois, “Rotating stall in the 
vaneless of a radial flow pump”, Procceedings of the 8th iInternational Symposium on Experimental and 
Computational  Aerothermodynamics of Internal Flows, Lyon, July 2007, paper ISAIF8-00102 
[7] G. Cavazzini, P. Dupont, G. Pavesi, A. Dazin, G. Bois, A. Atif, P. Cherdieu, “Analysis of unsteady flow 
velocity fields inside the impeller of a radial flow pump : PIV measurements and numerical calculation 
comparisons”, Proc. of ASME-JSME-HSME Joint fluids engineering conference 2011, July 24-29, 2011, 
Hamamatsu, Japan 
[8] G. Cavazzini, G. Pavesi, G. Ardizzon, P. Dupont, S. Coudert, G. Caignaert, G. Bois “Analysis of the 
rotor-stator interaction in a radial flow pump, Houille blanche – revue internationale de l’eau, 2009 
[9] G. Cavazzini, “Experimental and numerical investigation of the rotor-stator interaction in radial 
turbomachines”, Ph.D. thesis, University of Padova, Padova, Italy, 2006 
[10] G. Wuibaut, « Etude par vélocimétrie par images de particules des interactions roue-diffuseur dans une 
pompe centrifuge », PhD thesis, Thèse de Doctorat Ensam, 2001 


Numerical and experimental investigations in a vaned diffuser of SHF impeller

Abstract

Similar works

Full text

Available Versions

I-Revues